Question: Solve for $x$ and $y$ using substitution. ${3x+3y = -3}$ ${y = 5x+11}$
Explanation: Since $y$ has already been solved for, substitute $5x+11$ for $y$ in the first equation. ${3x + 3}{(5x+11)}{= -3}$ Simplify and solve for $x$ $3x+15x + 33 = -3$ $18x+33 = -3$ $18x+33{-33} = -3{-33}$ $18x = -36$ $\dfrac{18x}{{18}} = \dfrac{-36}{{18}}$ ${x = -2}$ Now that you know ${x = -2}$ , plug it back into $\thinspace {y = 5x+11}\thinspace$ to find $y$ ${y = 5}{(-2)}{ + 11}$ $y = -10 + 11$ $y = 1$ You can also plug ${x = -2}$ into $\thinspace {3x+3y = -3}\thinspace$ and get the same answer for $y$ : ${3}{(-2)}{ + 3y = -3}$ ${y = 1}$